Widely used in, for example, an an automobile assembly line and the like, is a grommet composed of a head portion having a screw hole defined through its center. Locking claws are disposed on the lower surface of the head portion. The locking claws are expanded when a screw is threaded in the screw hole. The grommet, however, is conventionally inserted by hand into a corresponding mounting hole of a member or workpiece screw is then screwed into the grommet. Thus, the speed of the line is difficult to increase because the grommet insertion is carried out by hand.
To cope with this problem, it has been attempted to hold the grommet by the extreme end of a robot arm and automatically insert it into a mounting hole. However, whether the grommet is accurately inserted into a mounting hole by the robot arm is unknown. Therefore, a means to determine whether the grommet is accurately inserted must be solved in order to develop a method for automatically inserting a grommet into a workpiece.